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DHCP-relay via unnumbered interfaces

 
 
Arjan
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      07-20-2004
Hi all,

I've got a setup with two 1721 routers, connected via DSL. Both routers
have a /32 on lo0 and a /29 on fas0. One of the routers has a DHCP
attached to fas0, one of of them is a relay-agent and has "ip
helper-address" (pointing to dhcp server) configured on fas0, that has a
laptop attached to it, trying to obtain a DHCP lease from the non-attached
router. (using build-in ios dhcp for lab purposes, the real-life setup
uses a seperate server). Both routers are running the latest IOS
(c1700-ipbase-mz.123-9.bin).

The problem: there seems to be an issue with IOS and relay via unnumbered
interfaces. I've noticed bug CSCds21050 and I've also noticed this cco
page:

http://www.cisco.com/univercd/cc/td/...2/dt_dhcpu.htm

This indicates that "ip helper-address" should also be set on the incoming
unnumbered interface. I've tried both with and without this extra helper
address.

However: the dhcp request that arrives on the server is broken. In the IP
header there is source address is 0.0.0.0, in the DHCP packet the
relay-agent field shows the same.

In a different setup with a numbered link between two routers (actually
two 806 boxes) this works fine and the DHCP traffic will pass the relay
agent.

Any comments/tips?

--
SSDD : http://www.vanderoest.net
 
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